close

Вход

Забыли?

вход по аккаунту

?

DESCRIPTION JP2012147115

код для вставкиСкачать
Patent Translate
Powered by EPO and Google
Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2012147115
The present invention provides an acoustic transducer capable of converting sound waves into a
plurality of electrical signals and suppressing variations in acoustic characteristics. An acoustic
sensor (11) has a vibrating film (22) and a fixed film (23) formed on the upper surface of a
semiconductor substrate (21), and changes in capacitance between the vibrating electrode (220)
in the vibrating film and a fixed electrode (230) in the fixed film. Thus, the sound wave is
converted into an electric signal and output. In the acoustic sensor 11, at least one of the
vibrating electrode 220 and the fixed electrode 230 is divided, and a plurality of divided
electrodes respectively output a plurality of electrical signals. [Selected figure] Figure 1
Acoustic transducer and microphone using the acoustic transducer
[0001]
The present invention relates to an acoustic transducer that converts sound waves into electrical
signals, and a microphone using the acoustic transducer. In particular, the present invention
relates to a micro-sized acoustic transducer or the like manufactured using MEMS (Micro Electro
Mechanical System) technology.
[0002]
Conventionally, ECM (Electret Condenser Microphone) has been widely used as a small
microphone mounted on a mobile phone or the like. However, since the ECM is weak to heat, and
11-04-2019
1
the MEMS microphone is superior in terms of digitalization, miniaturization, high functionality
and multifunctionality, and power saving, the MEMS microphone is now popularized. It is on the
way.
[0003]
The MEMS microphone detects a sound wave and converts it into an electric signal (detection
signal). The capacitor type acoustic sensor (acoustic transducer), a drive circuit for applying a
voltage to the acoustic sensor, and detection signals from the acoustic sensor And a signal
processing circuit that performs signal processing such as amplification and outputs the signal to
the outside. The acoustic sensor is manufactured using MEMS technology. Further, the drive
circuit and the signal processing circuit are integrally manufactured as an application specific
integrated circuit (ASIC) by using a semiconductor manufacturing technology.
[0004]
Recently, microphones have been required to detect and output loud sounds with high quality. In
general, the maximum input sound pressure (dynamic range) is referred to as “THD” in the
total harmonic distortion (Total Harmonic Distortion). Limited by). This is because, when a large
sound is to be detected by a microphone, harmonic distortion occurs in the output signal, and the
sound quality is impaired. Therefore, if the THD can be reduced, the maximum input sound
pressure can be increased.
[0005]
However, in a general microphone, the detection sensitivity of the sound wave and the THD are
in a trade-off relationship. Therefore, the high sensitivity microphone has a large THD, and the
maximum input sound pressure is reduced. This is because a high sensitivity microphone has a
large output signal and THD is easily generated. On the other hand, the low sensitivity
microphone has a smaller THD and a larger maximum input sound pressure. However, low
sensitivity microphones have difficulty in detecting small sounds with high quality.
[0006]
For such problems, microphones using a plurality of acoustic sensors having different detection
11-04-2019
2
sensitivities have been studied (see, for example, Patent Documents 1 to 4).
[0007]
Patent Documents 1 and 2 disclose microphones provided with a plurality of acoustic sensors,
and switching or fusing a plurality of signals from the plurality of acoustic sensors according to
the sound pressure.
In particular, Patent Document 1 switches between a high sensitivity acoustic sensor having a
detectable sound pressure level (SPL) of 20 dB to 110 dB and a low sensitivity acoustic sensor
having a detectable sound pressure level of 50 dB to 140 dB. By utilizing the microphone, a
microphone having a detectable sound pressure level of 20 dB to 140 dB is disclosed. Further,
Patent Documents 3 and 4 disclose configurations in which a plurality of independent acoustic
sensors are formed on one chip.
[0008]
U.S. Patent Application Publication No. 2009/03316916 (published on December 24, 2009) U.S.
Patent Application Publication No. 2010/0183167 (published on July 22, 2010) JP 2008245267 A (2008) US Patent Application Publication No. 2007/0047746 (released on March 01,
2007)
[0009]
However, in the case of the above-mentioned composition given in patent documents 3 and 4,
since each acoustic sensor is formed independently, respectively, variation and mismatching will
occur in acoustic characteristics.
Here, the variation in acoustic characteristics refers to the difference between the acoustic
characteristics of the acoustic sensors among the chips. Further, the mismatching of the acoustic
characteristics refers to the difference between the acoustic characteristics of a plurality of
acoustic sensors in the same chip.
[0010]
11-04-2019
3
Specifically, in each acoustic sensor, variations among chips regarding detection sensitivity occur
independently due to variations in warpage of a thin film to be formed. As a result, the variation
between chips with respect to the difference in detection sensitivity between acoustic sensors
becomes large. In addition, since each acoustic sensor is formed with a back chamber and a vent
hole separately, the acoustic characteristics such as frequency characteristics and phase affected
by the back chamber and the vent hole are mismatched in the chip. It will be.
[0011]
The present invention has been made in view of the above problems, and its object is to convert a
sound wave into a plurality of electrical signals and to suppress inter-chip variation and acoustic
mismatch in the chip with respect to acoustic characteristics. It is in providing an acoustic
transducer etc.
[0012]
In the acoustic transducer according to the present invention, a vibrating film and a fixed film are
formed on the upper surface of a substrate, and a sound wave is detected by a change in
capacitance between the vibrating electrode in the vibrating film and the fixed electrode in the
fixed film. In an acoustic transducer that converts and outputs an electric signal, at least one of
the vibrating electrode and the fixed electrode is divided in order to solve the above problem, and
a plurality of divided electric electrodes output a plurality of electric signals. It is characterized
by
[0013]
According to the above configuration, by dividing at least one of the vibrating electrode and the
fixed electrode, a plurality of variable capacitors are formed between the vibrating electrode and
the fixed electrode.
Therefore, an acoustic transducer capable of converting a sound wave into a plurality of electric
signals can be realized by outputting a plurality of electric signals from the plurality of divided
electrodes.
[0014]
11-04-2019
4
Further, the plurality of variable capacitors are formed in the same vibrating film and fixed film.
Therefore, compared with the prior art in which a plurality of diaphragms and fixed films are
formed independently, each variable capacitor has similar inter-chip variation in detection
sensitivity, and as a result, the detection sensitivity between the above-mentioned variable
capacitors Between chips in relation to the difference in In addition, each variable capacitor
shares the vibrating film and the fixed film, and as a result, it is possible to suppress the in-chip
mismatching relating to acoustic characteristics such as frequency characteristics and phase.
[0015]
Preferably, the variable capacitors have different detectable sound pressure levels. Thus, the
acoustic sensor including the plurality of variable capacitors can expand the detectable sound
pressure level as compared to the conventional acoustic sensor including only one variable
capacitor.
[0016]
In order to make the detectable sound pressure level of each variable capacitor different, for
example, at least two of the plurality of divided electrodes may have different sensitivities of
detecting the sound wave.
[0017]
Alternatively, at least two of the plurality of divided electrodes may have different areas.
Further, among the electrodes having different areas, the area of the vibrating film corresponding
to the wider electrode has a larger average value of the amplitude of vibration by the sound wave
than the area of the vibrating film corresponding to the narrower electrode. It should be made to
become. In this case, the detectable sound pressure levels can be further differentiated, and the
detectable sound pressure levels can be further expanded.
11-04-2019
5
[0018]
In addition, as the number of divided electrodes increases, it is necessary to increase wiring for
transmitting a signal from the electrode, an electric circuit for processing the signal, and the like,
and the size of the acoustic transducer and the microphone increases. It will be. Accordingly, the
plurality of divided electrodes is preferably a small number of divided electrodes, for example,
two electrodes divided into two.
[0019]
In the acoustic transducer according to the present invention, the distance between the vibrating
electrode and the fixed electrode is preferably constant. In this case, since each variable capacitor
has the same interval between the vibrating electrode and the fixed electrode, it is possible to
further suppress the in-chip mismatching related to the acoustic characteristic. In addition, the
formation of the vibrating electrode and the fixed electrode in the manufacturing process of the
acoustic transducer can be simplified.
[0020]
In the acoustic transducer according to the present invention, it is preferable that one of the
vibrating electrode and the fixed electrode be divided. In this case, since the number of
connections with external circuits is reduced compared to the case where both are divided,
productivity is improved. In addition, since the number of external connection terminals is
reduced, the parasitic capacitance due to the connection terminals can be reduced to improve the
characteristics. Further, since only one voltage is applied from the external charge pump, the size
of the external circuit including the charge pump can be reduced, the manufacturing cost can be
reduced, and the detection sensitivity due to the variation in the formation of the external charge
pump Variation of the difference between
[0021]
Even when both the vibrating electrode and the fixed electrode are divided, the same effect as
described above is obtained as long as the divided electrode of one of the vibrating electrode and
the fixed electrode is electrically shorted.
11-04-2019
6
[0022]
In the acoustic transducer according to the present invention, each of the vibrating electrode and
the fixed electrode preferably has a uniform thickness.
In this case, it is possible to further make the chip-to-chip variations relating to the detection
sensitivity of the variable capacitors due to manufacturing variations, and to further suppress the
chip-to-chip variations relating to the detection sensitivity differences between the variable
capacitors.
[0023]
In the acoustic transducer according to the present invention, the vibrating membrane may have
a rectangular base. Since the chip is generally rectangular, in the case of the above configuration,
the area on the chip can be used effectively. In addition, since the fixed portion between the
vibrating membrane and the substrate can be variously changed as compared with the vibrating
membrane having a circular base, the detection sensitivity can be variously changed. Further, as
compared with a vibrating membrane having a circular base, the deformation of the vibrating
membrane when a sound wave arrives is closer to a parallel plate shape, and the linearity of the
capacity change with respect to the sound pressure is improved.
[0024]
In the acoustic transducer according to the present invention, the vibrating membrane may have
a circular base. In this case, since stress concentration generated in the vibrating film can be
reduced as compared with the vibrating film having a rectangular base, durability against
external stress and internal stress is enhanced.
[0025]
In the acoustic transducer according to the present invention, the vibrating membrane preferably
includes an extending portion extending outward from the base, and is preferably fixed to the
substrate or the fixed film at the extending portion. In this case, the displacement of the
11-04-2019
7
diaphragm can be increased.
[0026]
In the acoustic transducer according to the present invention, the vibrating membrane may have
a slit formed in the boundary region of the divided vibration electrodes or in the region facing
the boundary region of the divided fixed electrodes. The difference between the displacement
amounts of the vibrating films is increased for the plurality of variable capacitors by the slits, so
that the difference in detection sensitivity can be increased. Further, since air flows in and out
through the slit, it is possible to suppress the fluctuation of the air pressure due to the vibration
of the vibrating film, and to suppress the fluctuation of the characteristics due to the fluctuation
of the air pressure.
[0027]
The width of the slit is preferably 10 μm or less. In this case, significant deterioration of the low
frequency characteristics can be suppressed.
[0028]
In the acoustic transducer according to the present invention, it is preferable that an air gap be
present between the vibrating membrane and the substrate. In this case, the displacement of the
vibrating membrane can be increased and the detection sensitivity can be improved as compared
with the configuration in which the air gap does not exist. In addition, even if the substrate is
distorted by an external force or the like, the vibrating film is not easily distorted, so that the
acoustic characteristics hardly change. In addition, the influence of fluctuations in external
pressure can be mitigated.
[0029]
In the acoustic transducer according to the present invention, in the vibrating membrane, at least
two of the plurality of regions corresponding to the plurality of divided electrodes are the area
ratio to the region of the fixed portion fixed to the substrate or the fixed film. May be different.
11-04-2019
8
[0030]
Generally, the displacement of the vibrating membrane relative to the sound pressure changes
depending on the shape of the fixed portion.
For example, as the number of fixed parts increases, the displacement with respect to the sound
pressure decreases, and the detection sensitivity decreases. Therefore, in the case of the above
configuration, the plurality of variable capacitors can be made to have different detection
sensitivities due to the difference in the area ratio.
[0031]
In the acoustic transducer according to the present invention, the substrate may be provided with
an opening in a region facing the central portion of the vibrating film, and a sound wave may be
incident from the opening. In this case, since the variable capacitors share the opening, it is
possible to further suppress the in-chip mismatching related to the acoustic characteristics such
as frequency characteristics and phase. Further, since the sound wave is incident from the
opening, deterioration of the sensitivity and the frequency characteristic due to the volume effect
of the opening can be suppressed as compared with the case where the sound wave is incident
from the fixed film.
[0032]
The same effects as described above can be obtained as long as the microphone includes the
acoustic transducer having the above-described configuration and an IC that supplies power to
the acoustic transducer and amplifies the electrical signal from the acoustic transducer and
outputs the signal to the outside. be able to.
[0033]
As described above, in the acoustic transducer according to the present invention, by dividing at
least one of the vibrating electrode and the fixed electrode, a plurality of variable capacitors are
formed between the vibrating electrode and the fixed electrode. By outputting the plurality of
electric signals from the plurality of divided electrodes, an acoustic transducer capable of
converting a sound wave into a plurality of electric signals can be realized.
11-04-2019
9
Further, since the plurality of variable capacitors are formed in the same vibrating film and fixed
film, it is possible to suppress inter-chip variations related to differences in detection sensitivity
among the variable capacitors, and to control the in-chip related to acoustic characteristics such
as frequency characteristics and phase. The effect of suppressing the mismatching of the variable
capacitor of
[0034]
It is the top view and sectional drawing which show schematic structure of the acoustic sensor in
the MEMS microphone which is one Embodiment of this invention. It is the top view and
sectional drawing which show the schematic structure of the said MEMS microphone. It is a
circuit diagram of the above-mentioned MEMS microphone. It is the top view and sectional
drawing which show schematic structure of the acoustic sensor in the MEMS microphone which
is another embodiment of this invention. It is a top view which shows schematic structure of the
acoustic sensor in the MEMS microphone which is another embodiment of this invention. It is a
top view which shows the vibration amount of the diaphragm of the said acoustic sensor. It is a
top view which shows schematic structure of the acoustic sensor in the MEMS microphone which
is another embodiment of this invention. It is a sectional view of the above-mentioned acoustic
sensor. It is a top view which shows schematic structure of the diaphragm in the said acoustic
sensor. It is an exploded view of the above-mentioned acoustic sensor. It is a graph which shows
the change of the average displacement amount of this vibrating film with respect to the sound
pressure applied to the vibrating film in the said acoustic sensor. It is a graph which shows the
typical frequency characteristic in a MEMS microphone. It is a top view which shows schematic
structure of the diaphragm in the acoustic sensor of the MEMS microphone which is other
embodiment of this invention. It is an exploded view of the above-mentioned acoustic sensor.
[0035]
First Embodiment An embodiment of the present invention will be described with reference to
FIGS. 1 to 3. FIG. 2 shows a schematic configuration of the MEMS microphone according to the
present embodiment, where (a) in the same figure is a plan view showing the top cut away, and
(b) and (c) in the same figure are front views It is a front view which notches a part and shows. In
addition, (c) of the figure is a modification of (b) of the figure.
11-04-2019
10
[0036]
As shown in FIG. 2, the MEMS microphone 10 is configured to include an acoustic sensor
(acoustic transducer) 11, an ASIC 12, a wiring board 13, and a cover 14.
[0037]
The acoustic sensor 11 detects a sound wave and converts it into an electric signal (detection
signal), and is a MEMS chip manufactured using MEMS technology.
The ASIC 12 is an IC having a power supply function of supplying power to the acoustic sensor
11 and a signal processing function of appropriately processing the electrical signal from the
acoustic sensor 11 and outputting the signal to the outside. The ASIC 12 is a semiconductor chip
manufactured using a semiconductor manufacturing technology. The acoustic sensor 11 and the
ASIC 12 are disposed on the wiring board 13 and covered by a cover 14.
[0038]
The electrical connection between the wiring substrate 13 and the acoustic sensor 11 and the
ASIC 12 is typically performed by the gold wire 15, but may be performed by gold bump bonding
or the like. Further, the wiring substrate 13 is provided with connection terminals 16 for
electrically connecting to the outside. The connection terminal 16 is used for external power
supply, external signal output, and the like. The wiring substrate 13 is attached to various
devices, typically by surface reflow mounting, and is electrically connected by the connection
terminals 16.
[0039]
The cover 14 has a function of protecting the acoustic sensor 11 and the ASIC 12 from external
noise, physical contact, and the like. For this reason, the cover 14 is provided with an
electromagnetic shield layer on the surface or inside. Further, in the cover 14, a through hole 17
is formed in order to allow an acoustic wave from the outside to reach the acoustic sensor 11.
Although the through hole 17 is formed on the upper surface of the cover 14 in (b) of FIG. 2, it
may be formed on the side surface of the cover 14 or, as shown in (c) of FIG. At 13, it may be
formed in the area where the acoustic sensor 11 is provided.
11-04-2019
11
[0040]
FIG. 1 shows a schematic configuration of the acoustic sensor 11 in the present embodiment, (a)
of the same figure is a plan view, and (b) of the same figure is an AA of (a) of the same figure. It is
the figure which cut | disconnected the line and was seen in the arrow direction.
[0041]
As shown in FIG. 1, in the acoustic sensor 11, a vibrating film 22 is provided on the upper
surface of the semiconductor substrate 21, and a fixing film 23 is further provided to cover the
vibrating film 22.
The vibrating film 22 is a conductor and functions as a vibrating electrode 220. On the other
hand, the fixed film 23 is composed of a fixed electrode 230 which is a conductor and a
protective film 231 which is an insulator for protecting the fixed electrode 230. The vibrating
electrode 220 and the fixed electrode 230 face each other via an air gap and function as a
capacitor.
[0042]
The edge of the vibrating film 22 is attached to the semiconductor substrate 21 via the insulating
layer 30. The insulating layer 30 is discretely and uniformly disposed between the edge of the
vibrating membrane 22 and the semiconductor substrate 21. Thus, a void (a vent hole) is present
between the edge of the vibrating film 22 and the semiconductor substrate 21.
[0043]
In addition, the semiconductor substrate 21 has an opening (back chamber) 31 in which a region
facing the central portion of the vibrating film 22 is opened. Moreover, the fixed film 23 has
many sound hole parts 32 in which the sound hole was formed. In general, the sound holes 32
are regularly arranged at equal intervals, and the size of the sound holes of each sound hole 32 is
approximately equal.
11-04-2019
12
[0044]
In the case of (b) of FIG. 2, the sound wave passes through the through hole 17 and the sound
hole 32 of the fixed film 23 and reaches the vibrating film 22. Further, in the case of (c) in the
same figure, typically, the through hole 17 and the opening 31 of the acoustic sensor 11 are
connected, and the sound wave passes through the through hole 17 and the opening 31 and
vibrates. The membrane 22 will be reached. In this case, compared with the case of (b) of the
same figure, the characteristic deterioration of the sensitivity and the frequency characteristic
due to the volume effect of the opening 31 can be suppressed.
[0045]
In the acoustic sensor 11 configured as described above, sound waves from the outside reach the
diaphragm 22 through the sound hole 32 or the opening 31 of the fixed film 23. At this time,
since the vibrating film 22 vibrates by applying the sound pressure of the reached sound wave,
the distance (air gap) between the vibrating electrode 220 and the fixed electrode 230 changes,
and the vibrating film 22 is moved between the vibrating electrode 220 and the fixed electrode
230 The capacitance changes. By converting the change in capacitance into a change in voltage
or current, the acoustic sensor 11 can detect an external sound wave and convert it into an
electrical signal (detection signal).
[0046]
In the acoustic sensor 11 configured as described above, the fixed film 23 has a large number of
sound holes 32. As described above, the sound holes 32 allow sound waves from the outside to
pass through and reach the vibrating film 22. Besides the above, it works as follows. (1) Since the
sound wave reaching the fixed film 23 passes through the sound hole 32, the sound pressure
applied to the fixed film 23 is reduced. (2) Since the air between the vibrating membrane 22 and
the fixed membrane 23 moves in and out through the sound hole 32, the thermal noise (the
fluctuation of air) is reduced. Further, since the damping of the vibrating membrane 22 due to
the air is reduced, the deterioration of the high frequency characteristics due to the damping is
reduced. (3) When forming a space between the vibrating electrode 220 and the fixed electrode
230 using surface micromachining technology, it can be used as an etching hole.
11-04-2019
13
[0047]
In the embodiment, the semiconductor substrate 21 is a semiconductor having a thickness of
about 400 μm and produced from single crystal silicon or the like. The vibrating film 22 has a
thickness of about 0.7 μm, is a conductor produced from polycrystalline silicon or the like, and
functions as a vibrating electrode 220. The fixed film 23 is composed of a fixed electrode 230
and a protective film 231. The fixed electrode 230 has a thickness of about 0.5 μm and is a
conductor made of polycrystalline silicon or the like. On the other hand, the protective film 231
has a thickness of about 2 μm and is an insulator produced from silicon nitride or the like. In
addition, the gap between the vibrating electrode 220 and the fixed electrode 230 is about 4
μm.
[0048]
In the present embodiment, as shown in FIG. 1, the fixed electrode 230 is divided into a central
electrode 230 a provided at the central portion of the fixed film 23 and a peripheral electrode
230 b provided at the peripheral portion of the fixed film 23. Electrically isolated. The central
electrode 230a is connected to the connection terminal 29a via the contact portion 27a and the
wiring 28a. On the other hand, the peripheral electrode 230b is connected to the connection
terminal 29b via the contact portion 27b and the wiring 28b. The vibrating electrode 220 is
connected to the connection terminal 26 through the wire 25.
[0049]
Thus, the capacitor is divided into a central capacitor that functions by the central portion of the
central electrode 230 a and the vibrating electrode 220 and a peripheral capacitor that functions
by the peripheral portion of the peripheral electrode 230 b and the vibrating electrode 220.
Accordingly, the acoustic sensor 11 of the present embodiment can convert an external sound
wave into an electrical signal from the central capacitor and an electrical signal from the
peripheral capacitor.
[0050]
Further, since the vibrating membrane 22 is fixed at the edge, the vibration displacement of the
11-04-2019
14
central portion is large and the vibration displacement of the peripheral portion is small. Thus,
the central capacitor becomes a high sensitivity capacitor with high detection sensitivity, and the
peripheral capacitor becomes a low sensitivity capacitor with low detection sensitivity. Therefore,
the acoustic sensor 11 of the present embodiment can convert an external sound wave into two
electric signals having different detection sensitivities. Thereby, the detectable sound pressure
level can be expanded as compared with the conventional acoustic sensor including only one
variable capacitor. Furthermore, the central electrode 230a has a larger area than the peripheral
electrode 230b. Thereby, the detectable sound pressure level can be further expanded.
[0051]
Further, in the present embodiment, although the fixed electrode 230 is divided, the vibrating
film 22 and the protective film 231 are common. Therefore, in the acoustic sensor 11 of the
present embodiment, the variation between chips regarding the detection sensitivity of the center
capacitor and the peripheral capacitor is similar to that of the conventional acoustic sensor in
which the vibrating membrane and the protective film are separate. As a result, it is possible to
suppress chip-to-chip variations related to the difference in detection sensitivity between the
center capacitor and the peripheral capacitor.
[0052]
Further, the central capacitor and the peripheral capacitor share the vibrating film 22 and the
protective film 231. As a result, it is possible to suppress in-chip mismatching relating to acoustic
characteristics such as frequency characteristics and phase. Furthermore, since the central
capacitor and the peripheral capacitor share the back chamber, the air gap, and the vent hole, it
is possible to further suppress the in-chip mismatching related to the acoustic characteristics.
[0053]
By the way, in the case of the above-mentioned composition given in patent documents 3 and 4,
since a plurality of independent acoustic sensors are formed in one chip, chip size becomes large.
In addition, since the number and length of wiring from each acoustic sensor to the ASIC
increase, parasitic capacitance and parasitic resistance increase, and characteristics (for example,
detection sensitivity, SNR (signal to noise ratio), etc.) deteriorate.
11-04-2019
15
[0054]
On the other hand, in the present embodiment, since the central capacitor and the peripheral
capacitor are formed in the vibrating film 22 and the fixed film 23, it is possible to suppress an
increase in chip size as compared with the prior art. In addition, since the length of the wiring
can be suppressed, deterioration of various characteristics can be suppressed.
[0055]
Further, in the present embodiment, the air gap when the vibrating membrane 22 is stationary is
constant. As a result, since the center capacitor and the peripheral capacitor have the same
distance between the vibrating electrode 220 and the fixed electrode 230, it is possible to further
suppress the in-chip mismatching relating to the acoustic characteristics. In addition, the
formation of the vibrating electrode 220 and the fixed electrode 230 in the manufacturing
process of the acoustic sensor 11 can be simplified.
[0056]
Further, in the present embodiment, each of the vibrating electrode 220 and the fixed electrode
230 is formed with a uniform thickness. This makes it possible to further make the chip-to-chip
variations with respect to the detection sensitivity of the center capacitor and the peripheral
capacitor due to manufacturing variations, and further to make the chip-to-chip variation with
respect to the difference in detection sensitivity between the center capacitor and the peripheral
capacitor It can be suppressed.
[0057]
Further, in the present embodiment, since the base of the vibrating membrane 22 is circular,
stress concentration occurring in the vibrating membrane 22 can be reduced as compared with
the case where the base of the vibrating membrane is rectangular. As a result, the resistance to
external stress and internal stress is enhanced.
11-04-2019
16
[0058]
Further, in the present embodiment, since the vent holes are present, the displacement of the
vibrating membrane 22 can be increased as compared with the configuration in which the vent
holes are not present, and the detection sensitivity can be improved. Further, even if the
semiconductor substrate 21 is distorted by an external force or the like, the vibrating film 22 is
not easily distorted, so that the acoustic characteristics are hardly changed. In addition, the
influence of fluctuations in external pressure can be mitigated.
[0059]
In the method of manufacturing the acoustic sensor 11 according to the present embodiment,
only the shape of the mask for separately forming the center electrode 230a and the peripheral
electrode 230b in the fixed electrode 230 is changed as compared with the conventional method
of manufacturing the acoustic sensor. Others are similar.
[0060]
That is, first, a sacrificial layer (SiO 2) is formed on the upper surface of a single crystal silicon
substrate to be the semiconductor substrate 21.
Next, a polycrystalline silicon layer is formed on the sacrificial layer and etching is performed to
form the vibrating film 22. Next, a sacrificial layer is formed again so as to cover the vibrating
membrane 22.
[0061]
Next, a polycrystalline silicon layer and a silicon nitride layer are formed so as to cover the
sacrificial layer, and etching is performed to form the fixed film 23 composed of the fixed
electrode 230 and the protective film 231. Here, the fixed electrode 230 is separated into the
central electrode 230a and the peripheral electrode 230b by forming the polycrystalline silicon
layer separately in the central portion and the peripheral portion by a mask pattern or the like.
[0062]
11-04-2019
17
Next, the opening 31 is formed by etching the single crystal silicon substrate. Then, by etching
the sacrificial layer through the sound hole 32, an air gap between the vibrating film 22 and the
fixed film 23 is formed, the insulating layer 30 is formed, and the acoustic sensor 11 is
completed.
[0063]
FIG. 3 is a circuit diagram of the MEMS microphone 10 shown in FIG. As shown in FIG. 3, the
acoustic sensor 11 is configured to include a low sensitivity variable capacitor 110 and a high
sensitivity variable capacitor 111 whose capacitance changes according to sound waves. The low
sensitivity variable capacitor 110 corresponds to the peripheral capacitor, and the high
sensitivity variable capacitor 111 corresponds to the central capacitor.
[0064]
The ASIC 12 is configured to include a charge pump 120, a low sensitivity amplifier 121, a high
sensitivity amplifier 122, a ΔΔ (Δ 型) type ADC (Analog-to-Digital Converter) 123 · 124, and a
buffer 125.
[0065]
The high voltage HV from the charge pump 120 is applied to the variable capacitors 110 and
111 of the acoustic sensor 11, whereby the sound waves are converted into electric signals by
the variable capacitors 110 and 111.
The electric signal converted by the low sensitivity variable capacitor 110 is amplified by the low
sensitivity amplifier 121 and converted into a digital signal by the ΔΔ type ADC 123. Similarly,
the electric signal converted by the high sensitivity variable capacitor 111 is amplified by the
high sensitivity amplifier 122 and converted into a digital signal by the ΔΔ type ADC 124. The
digital signal converted by the ΔΔ type ADCs 123 and 124 is output to the outside as a PDM
(pulse density modulation) signal through the buffer 125.
[0066]
11-04-2019
18
In the example of FIG. 3, the two digital signals converted by the ΔΔ type ADCs 123 and 124
are mixed and output on one data line, but the two digital signals are output on separate data
lines. You may
[0067]
In the present embodiment, the fixed electrode 230 is divided, and the vibrating electrode 220 is
not divided.
In this case, the number of connections with the ASIC 12 is reduced as compared to the case
where both the fixed electrode 230 and the vibrating electrode 220 are divided, so that the
productivity is improved. In addition, since the number of connection terminals with the ASIC 12
is reduced, it is possible to improve the characteristics by reducing the parasitic capacitance
caused by the connection terminals. Further, since only one voltage is applied from the charge
pump 120, the size of the ASIC 12 including the charge pump 120 can be reduced, the
manufacturing cost can be reduced, and the difference in detection sensitivity due to the
variation in generation of the charge pump 120 can be reduced. Can be reduced.
[0068]
Second Embodiment Next, another embodiment of the present invention will be described with
reference to FIG. FIG. 4 shows a schematic configuration of the acoustic sensor 11 according to
the present embodiment, where (a) of the figure is a plan view, and (b) of the figure is a B- of (a)
of the figure. It is the figure which cut | disconnected by B line and was seen in the arrow
direction.
[0069]
Compared with the acoustic sensor 11 shown in FIG. 1, the acoustic sensor 11 shown in FIG. 4
has a point that the insulating film 30 does not exist and the edge of the vibrating film 22 is not
fixed to the semiconductor substrate 21; The configuration is the same as that of the point that
the protrusions 232 protruding from the film 231 to the vibrating film 22 are discretely provided
along the peripheral electrode 230 b, and the other configuration is the same. In addition, the
same code | symbol is attached | subjected to the structure which has a function similar to the
11-04-2019
19
structure demonstrated in the said embodiment, and the description is abbreviate | omitted.
[0070]
The vibrating membrane 22 is not fixed to the semiconductor substrate 21, but when a voltage is
applied between the vibrating membrane 22 (the vibrating electrode 220) and the fixed electrode
230, the vibrating membrane 22 is held by the projection 232 by electrostatic force. Be done.
Thereby, the influence of the external stress or internal stress applied to the vibrating membrane
22 can be reduced. In addition, since the vibration in the peripheral portion of the vibrating
membrane 22 is restricted by the projection 232, the detection sensitivity of the peripheral
capacitor that functions by the peripheral electrode 230b and the peripheral portion of the
vibrating electrode 220 can be further lowered. As a result, the sensitivity difference between the
detection sensitivity of the center capacitor and the detection sensitivity of the peripheral
capacitors can be further increased.
[0071]
Third Embodiment Next, still another embodiment of the present invention will be described with
reference to FIG. 5 and FIG. FIG. 5 is a plan view showing a schematic configuration of the
acoustic sensor 11 according to the present embodiment. In the same figure, the protective film
231 of the fixed film 23 is omitted.
[0072]
The acoustic sensor 11 shown in FIG. 5 is different from the acoustic sensor 11 shown in FIG. 1
in the shape of the vibrating film 22 and therefore the shape of the fixed film is also different.
The other configurations are the same.
[0073]
The vibrating film 22 of the acoustic sensor 11 shown in FIG. 1 is circular, and is fixed to the
semiconductor substrate 21 at its edge. On the other hand, the vibrating membrane 22 of the
acoustic sensor 11 of the present embodiment has a substantially square base as shown in FIG. 5,
11-04-2019
20
and the corner portions 50 respectively extend outward from the center, It is fixed to the
semiconductor substrate 21 by the extension portion 51.
[0074]
FIG. 6 shows the amount of vibration of the vibrating membrane 22 when a predetermined sound
wave reaches the vibrating membrane 22 of the above configuration. In the same figure, it is
shown brighter as the amount of vibration increases. As illustrated, the vibrating membrane 22
has less vibration at the corner 50 and the extension 51. Therefore, as shown in FIG. 5, in the
fixed electrode 230 of the present embodiment, the fixed electrode 230 is substantially square,
the central portion is the central electrode 230a, and the corner portion and the connection
portion connecting the corner portions are It becomes a peripheral electrode 230b. As described
above, regardless of the shape of the vibrating membrane 22 (the vibrating electrode 220), the
central electrode 230a is formed to face the central region of the vibrating membrane 22, and
the peripheral electrode 230b is formed with the vibrating membrane 22. It may be formed to
face a region near the place fixed to the semiconductor substrate 21.
[0075]
In this embodiment, since the base of the vibrating membrane 22 is square, the area on the
rectangular chip can be effectively used. Further, compared to the vibrating film 22 having a
circular base, the fixing portion between the vibrating film 22 and the semiconductor substrate
21 can be variously changed, so that the detection sensitivity can be variously changed. Further,
as compared with the vibrating film 22 having a circular base, the deformation of the vibrating
film 22 when the sound wave arrives is closer to a parallel flat plate shape, and the linearity of
the capacity change with respect to the sound pressure is improved.
[0076]
Fourth Embodiment Next, still another embodiment of the present invention will be described
with reference to FIGS. FIG. 7 is a plan view showing a schematic configuration of the acoustic
sensor 11 according to the present embodiment, and FIG. 8 is a cross-sectional view taken along
the line C-C of FIG. FIG. 9 is a plan view showing a schematic configuration of the vibrating
membrane 22 in the acoustic sensor 11 of the present embodiment. FIG. 10 is an exploded view
of the acoustic sensor 11 according to the present embodiment. Note that, in FIG. 7, the
11-04-2019
21
protective film 231 of the fixed film 23 is illustrated only at the outline where it is installed with
the semiconductor substrate 21.
[0077]
The acoustic sensor 11 shown in FIGS. 7 to 10 has a point in which the vibrating membrane 22
and the fixed membrane 23 further extend laterally from the base as compared with the acoustic
sensor 11 shown in FIG. The separation configuration of the fixed electrode 230 is different, and
the other configurations are the same.
[0078]
The fixed electrode 230 of the fixed film 23 is provided with an extended electrode 230c in the
laterally extending portion which is laterally extended, instead of the peripheral electrode 230b.
That is, the fixed electrode 230 is divided into the central electrode 230a and the extended
electrode 230c. Similarly, instead of the contact portion 27b, the wire 28b, and the connection
terminal 29b, a contact portion 27c, a wire 28c, and a connection terminal 29c are provided. The
vibrating electrode 220 is connected to the connection terminal 26 via the contact portion 24
and the wire 25.
[0079]
The vibrating membrane 22 has the base wider than the lateral extension. Further, in the
vibrating membrane 22, the base portion is fixed at the fixing portion 51a at the tip end portion
of the extending portion 51, while the side extending portion is fixed at the fixing portion 52a at
the end portion 52 in the front-rear direction Be done. The portion not fixed at the edge of the
vibrating membrane 22 is a void (vent hole). That is, in the vibrating membrane 22, the area ratio
of the fixing portion 51a of the base to the area of the base is smaller than the area ratio of the
fixing portion 52a of the side extending portion to the area of the side extending portion. There
is. As a result, the base is displaced more than the side extension. In the example of FIG. 9, the
front right fixing portion 51a and the front fixing portion 52a are connected.
[0080]
11-04-2019
22
FIG. 11 is a graph showing the change in the average displacement for each region of the
vibrating membrane 22 with respect to the sound pressure applied to the vibrating membrane
22. The unit of sound pressure is Pa, and the unit of average displacement is μm. Referring to
the figure, it can be understood that the average displacement of the base is larger than that of
the lateral extension. Therefore, the variable capacitor formed by the above-mentioned base of
the vibrating membrane 22 and the central electrode 230a of the fixed film 23 functions as a
high sensitivity variable capacitor which can detect a small sound well.
[0081]
Further, referring to FIG. 11, in the graph of the base, the inclination of the average displacement
amount with respect to the sound pressure is constant until the sound pressure reaches 120 Pa,
but gradually decreases when the sound pressure exceeds 120 Pa I understand that. On the other
hand, in the graph of the side extending portion, it can be understood that the slope of the
average displacement amount with respect to the sound pressure is constant even when the
sound pressure reaches 200 Pa. Therefore, the variable capacitor formed by the abovementioned lateral extension of the vibrating film 22 and the extended electrode 230c of the fixed
film 23 functions as a low sensitivity variable capacitor capable of favorably detecting a loud
sound.
[0082]
Further, in the vibrating film 22, a slit 221 is formed so as to face the boundary region of the
central electrode 230 a and the extended electrode 230 c in the fixed film 23. In addition, since
the slit 221 is only formed in a part of the area facing the boundary area, the base and the
laterally extending portion are physically and electrically connected.
[0083]
By the way, when the slit 221 is not formed, the displacement of the base and the displacement
of the side extension are influenced with each other because the base and the side extension are
continuous. . On the other hand, in the present embodiment, since the slit 221 is formed, the
base and the laterally extending portion are divided in most parts, and the displacement of the
base and the displacement of the laterally extending portion The difference is more pronounced.
11-04-2019
23
[0084]
In addition, when the air pressure in the opening 31 and the air gap is different, air flows from
one of the opening 31 and the air gap to the other through the slit 221, so that the difference in
air pressure between the two can be reduced. . Therefore, it is possible to reduce the change of
the characteristics of the acoustic sensor 11 due to the change of the air pressure, and to reduce
the change of the characteristics due to the change of the external fluid, such as the wind noise,
and the noise.
[0085]
Note that if the width of the slit 221 is too wide, the ventilation effect becomes strong, and the
air leakage through the slit 221 becomes too large, which may lower the roll-off frequency and
deteriorate the low frequency characteristics. There is. This point will be described in detail
below.
[0086]
FIG. 12 shows typical frequency characteristics in a MEMS microphone. The vertical axis of the
figure is the frequency of the sound wave (unit: Hz), and the horizontal axis is the relative
sensitivity (unit: dBr). In the figure, the range in which the graph is horizontal is a range in which
the sound wave can be favorably detected because the relative sensitivity does not depend on the
frequency of the sound wave. The lower limit frequency of this range is the roll-off frequency
froll-off.
[0087]
In general, the roll-off frequency froll-off depends on the acoustic resistance Rventholl of the
ventilation hole and the compliance (air spring constant) Cbackchamber of air in the back
chamber (opening 31), and is expressed by the following equation.
froll−off∝1/(Rventholl×Cbackchamber) ・・・(1)。
11-04-2019
24
[0088]
The acoustic resistance Rventholl is also affected by the length of the slit 221, but decreases as
the width of the slit 221 is wider. Therefore, the roll-off frequency froll-off is increased according
to the equation (1), and as a result, the low frequency characteristic is deteriorated. For example,
when the width of the slit 221 is 1 μm, the roll-off frequency froll-off is 50 Hz or less, but when
it is 10 μm, it is 500 Hz. For this reason, when the width of the slit 221 exceeds 10 μm, the low
frequency characteristics are significantly deteriorated and the sound quality is impaired.
Therefore, the width of the slit 221 is preferably 10 μm or less.
[0089]
Fifth Embodiment Next, another embodiment of the present invention will be described with
reference to FIG. 13 and FIG. FIG. 13 is a plan view showing a schematic configuration of the
diaphragm 22 in the acoustic sensor 11 according to the present embodiment, and FIG. 14 is an
exploded view of the acoustic sensor 11 according to the present embodiment.
[0090]
As compared with the acoustic sensor 11 shown in FIGS. 7 to 10, in the acoustic sensor 11 of this
embodiment, the central electrode 230a and the extended electrode 230c of the fixed electrode
230 are connected, while the vibrating electrode 220 is the above-described base and The
difference is that the center electrode 220a and the extended electrode 220c are separated at the
side extension portion, and the other configuration is the same. Thus, the vibrating electrode 220
can also be separated. In this case, the central electrode 220 a and the extended electrode 220 c
are connected to the amplifiers 121 and 122 of the ASIC 12.
[0091]
The present invention is not limited to the above-described embodiments, and various
modifications can be made within the scope of the claims, and embodiments obtained by
appropriately combining the technical means disclosed in the different embodiments. Is also
included in the technical scope of the present invention.
11-04-2019
25
[0092]
For example, in the above embodiment, the sound hole 32 has a circular cross section, but may
have an arbitrary shape such as a triangle or a square.
[0093]
Further, in the above embodiment, one of the vibrating electrode 220 and the fixed electrode
230 is divided into two, but may be divided into three or more.
However, as the number of divided electrodes increases, it is necessary to increase the wiring for
transmitting the signal from the electrode, the electric circuit for processing the above signal in
the ASIC 12, etc. The size will increase.
Therefore, it is desirable that the number of divided electrodes be as small as, for example, two.
[0094]
Also, both the vibrating electrode 220 and the fixed electrode 230 may be divided. In this case,
according to the characteristics of the amplifiers 121 and 122 of the ASIC 12, one of the divided
electrodes of the vibrating electrode 220 and the fixed electrode 230 is connected to the
amplifiers 121 and 122, and the other divided electrodes are shorted. Good. Alternatively, a
plurality of charge pumps 120 of the ASIC 12 may be provided and connected to any one of the
divided electrodes, and the amplifiers 121 and 122 may be connected to the other divided
electrode.
[0095]
As described above, the acoustic transducer according to the present invention can suppress
variations in acoustic characteristics by realizing an acoustic transducer capable of converting
sound waves into a plurality of electrical signals in the same vibrating membrane and fixed
membrane. The present invention can be applied to any MEMS acoustic sensor.
[0096]
DESCRIPTION OF SYMBOLS 10 MEMS microphone 11 Acoustic sensor 12 ASIC 13 Wiring board
11-04-2019
26
14 Cover 15 Gold wire 16 Connection terminal 17 Through-hole 21 Semiconductor substrate 22
Vibrating film 23 Fixed film 24 Contact part 25 Wiring 26 Connection terminal 27 Contact part
28 Wiring 29 Connection terminal 30 Insulating layer Reference Signs List 31 opening 32 sound
hole 50 corner 51 extension 51a fixing portion 52 end 52a fixing portion 110 low sensitivity
variable capacitor 111 high sensitivity variable capacitor 120 charge pump 121 low sensitivity
amplifier 122 high sensitivity amplifier 123 · 124 ADC 125 buffer 220 vibration electrode 220 a
central electrode 220 c extended electrode 221 slit 230 fixed electrode 230 a central electrode
230 b peripheral electrode 230 c extended electrode 231 protective film 232 protrusion
11-04-2019
27
Документ
Категория
Без категории
Просмотров
0
Размер файла
42 Кб
Теги
description, jp2012147115
1/--страниц
Пожаловаться на содержимое документа